The present invention relates to an improved temperature probe for use in measuring or monitoring the temperature of fluid.
In the transporting of natural gas, which oftentimes comprises both gaseous components and liquid components, the natural gas is transported through a pipeline from a gas well or the like to a point of use or distribution. Irrespective of the size of such pipelines, they operate in substantially the same way. During the transporting of natural gas in pipelines, it has been found important to monitor certain variables regarding the condition of the natural gas. Monitored variables can include pressure, temperature, speed of flow and flow rate. These variables are important in order to determine not only the state of the natural gas, but the properties of the gas and its economic value. For example, its BTU value as delivered to a customer and the relative proportions of gaseous components to liquid components. The variables as measured, should provide as instantaneous and real time value for the variables as is practicable. This is particularly true when calculating the BTU value of the natural gas since natural gas is sold by its volume and BTU value (MMBtu). Even a small fraction of a percent in variation from the actual condition to the measured condition can equate to a potential significant decline in profits of the buyer or seller by failing to know the true BTU value of natural gas. The actual values are thus important for both buyer and seller with both oftentimes monitoring the natural gas and sometimes using an independent third party to monitor.
Many devices for monitoring variables, such as temperature and pressure of natural gas, are available from Welker Engineering of Sugar Land, Tex.
Much engineering work has gone into refining and improving the ability to monitor natural gas properties but improvements, even though minor in accuracy, are important in order to obtain more accurate information about the natural gas and hence its economic value. Further, durability and reliable functioning are important factors.
Two commercial temperature probes are Welker model AITP-1F and Model AITP-1S. Both of these probes are of the automatic insertion type which allows for an operator to selectively have the temperature sensing probe inside the pipeline (extended), or outside of the normal gas flow path of the pipeline (retracted) in the event pigging is desired for the pipeline. The retraction of the probe allows a pig to move unimpeded through the pipeline as is known in the art. The temperature sensing probe includes a sensor with a sensing element, such as a thermocouple, enclosed within a closed carrier rod for movement into and out of the pipeline and to protect the sensing element. The sensor typically has the sensing element enclosed in a tubular housing. Such housings are generally small, e.g., ⅛– 3/16 inch in diameter and can be made of metal or plastic depending on the application. The inside dimension of the housing is approximately equal to the exterior size of the sensing element and there is preferably contact between the sensing element and housing to improve heat transfer and to reduce the temperature gradient. Enclosing the sensor within a closed end carrier seals the interior of the pipeline from the exterior of the pipeline in a simple and effective manner. The enclosing of the sensor in a carrier also provides needed durability and functionality. The flowing gas can be moving as fast as 200 ft/sec and sometimes faster. The natural gas can also have entrained liquid that can impact on the carrier possibly setting up vibrations or causing damage. Also, the probes can be very long for the section that extends into the pipeline. The exposed portion of the probe must have sufficient structural properties, e.g., resistance to bending to withstand the forces applied thereto. They must resist damage from the impinging liquid and must also be resistant to vibration that can damage and even break the probe. A thermocouple sensor is on its own not well adapted for use in a natural gas pipeline because of its size and strength. To solve these problems, the industry has enclosed the sensor completely in a carrier. Enclosing provides the advantages of sealing against leakage from the conduit interior to its exterior, strength and protection of the sensor. The use of an enclosed sensor was considered to be acceptable. However, increased measurement accuracy and responsiveness is desired while still achieving the goals of sensor protection and sealing the interior of the pipeline from the exterior of the pipeline.
With prior art devices, if maintenance is needed, a significant amount of disassembly or possibly shutting down the pipeline was required in order to effect maintenance. This is costly as well as time consuming and presents dangers should there be residual pressure in the line allowing the natural gas to escape when parts of the devices are removed. The positioning of temperature sensors in the flow stream is effected by having the sensor pass through an isolation valve that is used to selectively isolate the interior of the pipeline from the probe device when the sensing element is retracted. This requires a valve assembly that allows the valve element to be open for the sensing element to be extended through, retracted from and remain in the extended position. To do maintenance work on the probe or to pig the line, the sensing element is retracted past the isolation valve, after which the isolation valve is closed to allow work on the insertion device, sensing element and/or pipeline. However, given the construction of currently available probes and insertion devices, it is not possible to eliminate the isolation valve on a line unless one is willing to shut the line down in order to effect maintenance on or installation of a monitoring device after the pipeline is constructed except during down periods on the pipeline.
Another problem is the expense of providing the insertion devices for extending and retracting the sensing element. Automatic insertion devices are available in two basic forms. The first form of device involves the use of a permanently attached gas or liquid powered linear motion cylinder drive and the entire device is attached to the pipeline or the like. However, each probe has a drive, and the drives are seldom used, resulting in a relatively large investment in drives. The second form of automatic insertion device uses a removable gas or liquid powered linear motion cylinder drive allowing the drive to be used at multiple locations thereby reducing the investment in drives. An example of a permanently attached drive is a Welker Model AID-1. Examples of removable drives are Welker Models AID-2 and AID-3.
Therefore, there is a need for an improved insertion device and sensing probe.